Gudgeon Pin

A gudgeon pin, widely known as a wrist pin in North America, is a precision-ground, hollow steel pin that connects the piston to the small end of the connecting rod. It acts as the pivot point around which the connecting rod oscillates as the piston moves up and down in the cylinder, transferring combustion force down to the rod.

Gudgeon pins are subjected to massive reciprocating forces and combustion heat. They are typically engineered as hollow tubes to minimize reciprocating mass while maintaining high shear strength. Depending on the design, gudgeon pins can be press-fit into the connecting rod (semi-floating) or held in place within the piston boss by retaining clips (full-floating), allowing the pin to rotate freely in both the rod and piston.

A worn gudgeon pin or loose retaining clip can lead to a metallic clicking or double-knock noise from the engine that is most noticeable at idle. If a pin breaks or a clip comes out, the pin will slide sideways and deeply score the cylinder wall, requiring an engine block sleeve or replacement. Proper lubrication from engine oil sprayed up from the crankshaft is vital for pin longevity.